Attached Files:

Noticed this as well in my game as Scotland against Roosevelt, there was a game wide Emergency which all the civs joined but I did not join yet one of his cities attacked mine, and his city states keep attacking me as well. We are not at war and no diplomatic change either.

You, gentlemen, are in need of great upheavals; we are in need of Great Russia. ~ Pyotr Stolypin

No man can sit down and withhold his hands from the warfare against wrong and get peace from his acquiescence. ~ Woodrow Wilson, 1911

Also against Tamar, we had been allies for centuries, from Medieval to Information. It dropped one turn, joint war dec against me with Teddy, still on her turn she asks me to be friends again. I renew alliance on my turn, but she is still at war with me and my city states. Got so annoyed I dropped the whole game.

Early man walked away as modern man took control.
Their minds weren't all the same, to conquer was his goal,
So he built his great empire and slaughtered his own kind,
Then he died a confused man, killed himself with his own mind​

Just experienced this myself. Was friendly with Lautaro even though he was invading my borders. Just made a Military Alliance with him and yet he's attacking my cities and plundering my trade routes, and I can even attack back!

In my last game I had a similar situation against Pedro. He was my ally but suddenly he joins a joint war against me together with France. In the UI France is marked as being at war with me. Pedro, however, is friendly, in fact we still have a friendship going. And when I enter diplomacy he agrees with a cultural alliance with me. So now we are allies again, though he's still attacking me and I can attack his troops.

Yes, that can happen if your "friend" declares a joint war against you and wants to renew your friendship in the same turn(!). Workaround: Don't accept friendship requests in the same turn someone declares war on you.